bug creations invoice

when creating an invoice, if an amount is entered in the unit price, the total does not change if the quantity is set to zero. if an amount was entered in the unit price and the quantity was set to zero, if the unit price is subsequently changed, no change is made to the total if the quantity remains at zero. this could result in something like 0 units at $0 total $340 or 0 units at $400 = $800.

thank you. have a nice day